New Flashcards
1
Q
What is a monomer?
A
A smaller, repeating molecule from which larger polymers are made
2
Q
What is a polymer?
A
A larger molecule which is made up of identical repeating monomers.
3
Q
What is a condensation reaction?
A
A reaction in which two molecules join together, forming a covalent bond and releasing a molecule of water.
4
Q
What is a hydrolysis reaction?
A
A reaction in which the covalent bond between two molecules is broken, which uses up a molecule of water.
5
Q
Which polymer consists of repeating nucleotides?
A
Polynucleotides (DNA or RNA)
6
Q
Which polymer consists of repeating monosaccharides?
A
Polysaccharides
7
Q
Which polymer consists of repeating amino acids?
A
Polypeptides (Proteins)
8
Q
What is the difference between alpha and beta glucose?
A
In α-glucose, the H is above the OH whereas in β-glucose, the OH is above the H
9
Q
Draw a molecule of alpha glucose.
A
https://static.aqa.org.uk/assets/image/0018/235440/00055366-DA00046397-DB.png
10
Q
Draw a molecule of beta glucose
A
https://static.aqa.org.uk/assets/image/0008/235439/00055366-DA00046396-DB.png
11
Q
What are isomers?
A
Molecules with the same molecular formula but differently arranged atoms.
12
Q
What are disaccharides and how are they formed?
A
A disaccharide is two monosaccharides joined together with a glycosidic bond. They are formed by a condensation reaction, which releases a molecule of water.
13
Q
Which disaccharide does Glucose and Glucose make?
A
Maltose
14
Q
Which monosaccharides make Maltose?
A
Glucose and Glucose
15
Q
Which disaccharide does Glucose and Fructose make?
A
Sucrose
16
Q
Which monosaccharides make Sucrose?
A
Glucose and Fructose
17
Q
Which disaccharide does Glucose and Galactose make?
A
Lactose
18
Q
Which monosaccharides make Lactose?
A
Glucose and Galactose
19
Q
What are polysaccharides and how are they formed?
A
Polysaccharides are made up of many (more than 2) monosaccharides, joined together with glycosidic bonds. They are formed by many condensation reactions, releasing water molecules.
20
Q
Describe the basic function and structure of starch.
A
Starch acts as an energy source in plant cells. It is a polysaccharide of alpha glucose. It contains both Amylose and Amylopectin. Amylose has 1-4 glycosidic bonds and is therefore unbranched. Amylopectin has both 1-4 and 1-6 glycosidic bonds, meaning that it is branched.
21
Q
Describe the basic function and structure of glycogen.
A
Glycogen acts as an energy store in animal cells. It is a polysaccharide of alpha glucose. It has both 1-4 and 1-6 glycosidic bonds. Therefore, it is branched.
22
Q
Describe the basic function and structure of cellulose.
A
Cellulose acts as structural support in plant cells. It is found in the cell walls of plant cells. It is a polysaccharide of beta glucose, held together by 1-4 glycosidic bonds forming straight unbranched chains. Chains are joined together with hydrogen bonds forming microfibrils.
23
Q
Explain how the structure of starch is related to its function.
A
Starch is helical, so it is compact for storage in cell. Also, it is a large molecule, meaning it can not leave the cell. It is also insoluble in water, meaning that it does not affect the water potential of the cell, so no osmotic action which could damage the cell occurs. Also, it is branched to increase the surface area for faster hydrolysis.
24
Q
Explain how the structure of glycogen is related to its function.
A
Glycogen is branched are is therefore compact and more molecules can fit in small area. Also, the branching results in a larger surface area for the enzymes to quickly hydrolyse the glycosidic bonds to release glucose. Also, it is a large molecule meaning it can not leave the cell. It is also insoluble in water, meaning that it does not affect the water potential of the cell, so no osmotic action which could damage the cell occurs
25
Explain how the structure of cellulose is related to its function.
Every second β-glucose molecule is inverted in a long, straight, unbranched chain. Many hydrogen bonds link parallel strands (crosslinks) to form microfibrils. Hydrogen bonds are strong in large quantities, so provides strength to plant cell walls
26
Describe the test for reducing sugars
Firstly, add Benedict’s solution, which is blue to the sample. Next, heat the sample in a water bath. A positive test will result in a green, yellow, orange or red precipitate depending upon on the concentration of reducing sugars.
27
Describe the test for non-reducing sugars.
If the result of the Benedict’s test is negative, there still could be non-reducing sugar present. Heat in a boiling water bath and add acid in order to hydrolyse into reducing sugars. Next, neutralise with alkali (e.g. sodium bicarbonate) Now, carry out the Benedicta test as normal by heating sample in a boiling water bath with Benedict’s solution. Positive result = green / yellow / orange / red precipitate.
28
What is the one example of a non reducing sugar (that’s on the specification)?
Sucrose
29
Suggest a method to measure the quantity of sugar in a solution without a colorimeter.
Carry out a Benedict’s test, then filter and dry the precipitate. Then, measure the mass of the precipitate.
30
Suggest a method to measure the quantity of sugar in a solution using a colorimeter.
First, make a dilution series of sugar solutions of known concentrations. Next, heat a set volume of each sample with a set volume of Benedict’s solution. Use a colorimeter to quantitively measure the absorbance of each known concentration, and plot a calibration curve with concentration on the x axis and absorbance on the y axis, and draw a line of best fit. Repeat the Benedict’s test with the unknown sample and find the concentration on the graph with is associated with the absorbance of the unknown sample.
31
Describe the biochemical test for starch.
Add iodine dissolved in potassium iodide, which is orange/brown. A positive result will cause a colour change to blue/black
32
Name 2 groups of Lipids
Triglycerides and Phospholipids
33
Describe the structure of a fatty acid.
Has a variable R Group which is a hydrocarbon chain which is either saturated or unsaturated. It also has a Carboxyl group.
34
What is the difference between saturated and unsaturated fatty acids?
Unsaturated fatty acids contain one or more Carbon-Carbon double bonds, creating kinks in the hydrocarbon chain. Saturated fatty acids contain no Carbon-Carbon double bonds, and therefore all Carbons are fully saturated with Hydrogen.
35
How do triglycerides form?
Triglycerides consist of 1 glycerol molecule and 3 fatty acids, which join via condensation reactions. Therefore, 3 molecules of water are released and 3 ester bonds form.
36
Explain how the properties of triglycerides are related to their structure.
The hydrolysis of the fatty acid chains releases a lot of energy, meaning that triglyceride molecules are ideal energy stores. Also, the fatty acid chains are hydrophobic, meaning that triglyceride molecules are insoluble in water. Therefore, the molecules do not affect water potential, so no osmotic action occurs, damaging cells.
37
Describe the difference between the structure of triglycerides and phospholipids.
One of the fatty acids of a triglyceride is substituted for a phosphate group in a phospholipid.
38
Describe how the properties of phospholipids relate to their structure.
The phosphate group is hydrophilic and the fatty acid chains are hydrophobic. Therefore they can form membranes as they are selectively permeable, allowing certain substances into the cell and not others.
39
Describe the test for lipids.
Add ethanol and shake, and then add water. If the test is positive, a milky emulsion will form on top.
40
Draw the general structure of an amino acid.
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.aqa.org.uk%2Fsubjects%2Fscience%2Fas-and-a-level%2Fbiology-7401-7402%2Fsubject-content%2Fbiological-molecules%2Fproteins&psig=AOvVaw0Ejp3i16r137YV3d00bXZM&ust=1711109171973000&source=images&cd=vfe&opi=89978449&ved=0CBAQjRxqFwoTCJiHjcyohYUDFQAAAAAdAAAAABAD
41
What is the molecular formula of the carboxyl group?
COOH
42
What is the molecular formula of the amine group?
NH₂
43
How many amino acids are common in all organisms and how do they vary?
There are 20 amino acids that are common in all organisms and they differ only in their R group side chain.
44
How do amino acids join together?
Amino Acids join together via a condensation reaction, removing a water molecule. A Peptide bond is formed between the carboxyl group of one amino acids and the amine group of the other.
45
What is a dipeptide?
2 amino acids joined together with peptide bonds.
46
What is a polypeptide?
More than 2 amino acids joined together with peptide bonds.
47
What is the primary structure of a protein?
Sequence of amino acids in a polypeptide chain, joined by peptide bonds.
48
What is the secondary structure of a protein?
The folding of the polypeptide chain into alpha helices or beta pleated sheets due to hydrogen bonding between amino acids (between NH group of one amino acid and C=O group of the other)
49
What is the tertiary structure of a protein?
The 3D folding of the polypeptide chain due to interactions between the R groups of the amino acids. Therefore, hydrogen bonds, ionic bonds and disulphide bridges are formed.
50
What is the quaternary structure of a protein?
Made up of more than one polypeptide chain, formed by interactions between polypeptides.
51
Describe the test for proteins.
Add Biuret reagent (sodium hydroxide + copper II sulphate), which is blue. A positive result will cause a colour change to lilac. This indicates the presence of peptide bonds and therefore the presence of proteins.
52
How do enzymes act as a biological catalyst?
Enzymes catalyse reaction by lowering the activation energy. This speeds up the rate of reaction as less energy is needed to start it.
53
Describe the lock and key model of enzyme action.
Substrate binds to the active site, which is completely complimentary to it. They bind to form an enzyme-substrate complex.
54
Describe the induced fit model of enzyme action.
The substrate binds to the active site, which is not completely complimentary. This causes the active site to change shape so that it becomes complimentary to the substrate and an enzyme-substrate complex forms. This causes bonds in the substrate to change, lowering activation energy.
55
How have models of enzyme action changed over time?
Initially, the accepted model of enzyme action was the lock and key model, which stated that the active site is fixed and it is exactly complimentary to the substrate. New molecular evidence has suggested the induced fit model, which states that the active site changes shape slightly in order for the substrate to be able to fit.
56
Explain the specificity of enzymes.
The specific tertiary structure determines the shape of the active site. This is dependent on the sequence of amino acids (primary structure). The active site is complimentary to a specific substrate, and only this substrate can bind to the active site. The active site slightly changes shape in order for the substrate to fit, forming an enzyme-substrate complex.
57
Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions.
As enzyme concentration increases, the rate of reaction also increases. At this point, enzyme concentration is the limiting factor and there is excess substrate. The rate increases because the concentration of enzymes is increasing, and there are more available active sites for substrate molecules to bind to, and therefore more enzyme-substrate complexes are formed. At a certain point, the substrate concentration becomes the limiting factor, so the rate will stop increasing because all of the substrates will be in use.
58
Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions.
As substrate concentration increases, the rate of reaction also increases. At this point, substrate concentration is the limiting factor and there is an excess of active sites. The rate increases because the concentration of substrates is increasing, and there are more substrate molecules that can bind to active sites, and therefore more enzyme-substrate complexes are formed. At a certain point, the enzyme concentration becomes the limiting factor, so the rate will stop increasing because all of the enzymes will be saturated.
59
Describe and explain the effect of temperature concentration on the rate of enzyme-controlled reactions.
As temperature increases up to the optimum, the rate of reaction increases because the molecules have more kinetic energy, meaning that more collisions between enzymes and substrate molecules will occur, leading to more enzyme-substrate complexes being formed. After the optimum, the rate of reaction decreases as the enzymes denature. Due to the high temperatures, the hydrogen bonds and ionic bonds in the tertiary structure of the enzyme break, changing the shape of the active site. Therefore, the active site is no longer complimentary, meaning that fewer enzyme-substrate complexes can form.
60
Describe and explain the effect of pH on the rate of enzyme-controlled reactions.
If the pH decreases or increases too much beyond the optimum, the rate of reaction decreases. This is because the H+ and OH- ions interfere with the hydrogen bonds and ionic bonds in the tertiary structure of the enzyme. Therefore, the shape of the active site changes and is no longer complimentary to the substrate, meaning that fewer enzyme-substrate complexes can form.
61
Describe and explain the effect of competitive inhibitors on the rate of enzyme-controlled reactions.
As the concentration of competitive inhibitors increases, the rate of reaction decreases. Competitive inhibitors have a similar shape to the substrate, and they therefore compete for the active site. This means that the active site is occupied, so the substrate can’t bind to the active site and fewer enzyme-substrate complexes can form. Increasing the concentration of substrate will reduce the effect of the competitive inhibitor as the substrate will begin to outcompete the inhibitor.
62
Describe and explain the effect of non-competitive inhibitors on the rate of enzyme-controlled reactions.
As the concentration of non-competitive inhibitor increases, the rate of reaction increases. Non-competitive inhibitors bind to the allosteric site, away from the active site. This leads to the tertiary structure of the enzyme changing, and the shape of the active site changing. Therefore, the active site is no longer complimentary to the substrate, so the substrate can not bind and fewer enzyme-substrate complexes form. Increasing substrate concentration will have no effect on the rate of reaction as the change to the tertiary structure is permanent.
63
Draw and label the general structure of a nucleotide.
https://images.squarespace-cdn.com/content/v1/5c5aed8434c4e20e953d6011/1600528627495-YZ3SZ4AQ5LOSINZEEX1I/nucleotide.jpg
64
Name 5 variables that could affect the rate of enzyme-controlled reaction.
Enzyme concentration, Substrate concentration, Temperature, pH, Inhibitor concentration.
65
What is the basic function of RNA in living cells?
Transfers genetic information from DNA to ribosomes.
66
What does a ribosome consist of?
RNA and Proteins
67
What is the basic function of DNA in living cells?
Carries genetic information, which codes for proteins.
68
Describe 3 differences between DNA and RNA.
In a DNA nucleotide, the pentose sugar in deoxyribose, whereas in RNA it is ribose. DNA contains the nitrogenous bases A, T, G and C, whereas RNA contains A, U, G and C. DNA molecules are double stranded and much larger than RNA molecules, which are much smaller and usually single stranded.
69
How do nucleotides join together to form polynucleotides?
Nucleotides join via condensation reactions, which remove water molecules. This forms phosphodiester bonds between the phosphate group of one nucleotide and the deoxyribose/ribose of the other.
70
Why did many scientists originally doubt that DNA carried the genetic code?
DNA is a chemically simplistic molecule which consists of very few components. Many scientists believed that the molecule that carries the genetic code would be much more complex.
71
Describe the structure of DNA.
DNA is a polynucleotide. Each nucleotide is formed from a deoxyribose pentose sugar, a phosphate group, and a nitrogenous base. Adjacent nucleotides are joined by phosphodiester bonds, and the 2 polynucleotide chains are joined by hydrogen bonds between complimentary base pairs (Adenine and Thymine, Guanine and Cytosine) This forms a double helix structure.
72
Describe the structure of RNA.
RNA is Polynucleotide. Each nucleotide is formed from a ribose pentose sugar, a phosphate group and a nitrogenous base (Adenine, Uracil, Guanine or Cytosine). Phosphodiester bonds join adjacent nucleotides, forming a single helix.
73
How does the structure of DNA relate to it’s function?
* Double stranded - Both can act as template strands for semi-conservative replication.
* Hydrogen bonds between complimentary base pairs are weak - strands can be easily separated for replication.
* Complimentary base pairing - Accurate replication
* Many hydrogen bonds between complimentary base pairs - strong, stable molecule
* Double helix with sugar phosphate back bone - protects the bases and hydrogen bonds
* Long molecule - can store lots of genetic information, which codes for proteins.
* Coiled double helix - compact for storage
74
How can you use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases?
The % of adenine in strand 1 is equal to the % of thymine in strand 2 and vice versa. The % of guanine in strand 1 is equal to the % of cytosine in strand 2 and vice versa. This is because of complimentary base pairing between the 2 strands.
75
How many hydrogen bonds are there between the 2 complimentary base pairings in DNA?
There are 2 Hydrogen bonds between Adenine and Thymine, and 3 Hydrogen bonds between Guanine and Cytosine
76
Why is semi-conservative replication important?
It ensures genetic continuity between generations of cells.
77
Why is DNA replication known as “semi-conservative”?
Each new DNA molecule consists of one strand from the parent DNA molecule, and one new strand.
78
Describe the process of semi-conservative DNA replication.
1. DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
2. Both strands act as template strands.
3. Free DNA nucleotides in the nucleoplasm are attracted to exposed bases and join by complementary base pairing
4. Hydrogen bonds form between complimentary base pairs (adenine-thymine and guanine-cytosine)
5. DNA Polymerase moves along the polynucleotide chain, joining adjacent nucleotides on new strand by condensation reactions, forming phosphodiester bonds.
79
Why does DNA Polymerase move in opposite directions along the polynucleotide chains?
DNA has antiparallel strands, so the arrangements of nucleotides on each end are different. DNA Polymerase is an enzyme, and therefore has a specific active site, so it can only bind to substrate with a complimentary shape, which is the Phosphate end of each strand.
80
Which two scientists proposed models of the chemical structure of DNA and DNA replication?
Watson and Crick
81
Describe the work of Meselson and Stahl in validating the Watson-Crick model of semi-conservative DNA replication.
1. Bacteria that was grown in medium containing heavy nitrogen (15N) -and nitrogen is incorporated into DNA bases. The DNA was extracted & centrifuged, so it settled near the bottom, as all DNA molecules contain 2 heavy strands
2. Bacteria that was grown in medium containing heavy nitrogen (15N) and was transferred to medium containing light nitrogen (14N) and was left to divide once - The DNA was extracted & centrifuged, so it settled in middle, as all DNA molecules contain 1 original heavy strand and 1 new light strand
3. Bacteria in light nitrogen (14N) allowed to divide again -
The DNA was extracted & centrifuged, and half settled in middle, as
contains 1 original heavy and 1 new light strand; half
settles near top, as contains 2 light strands.
82
What components make up ATP?
A ribose sugar, Adenine and 3 Phosphate groups.
83
How is ATP broken down?
ATP is broken down via a hydrolysis reaction, using a molecule of water. ATP → ADP + Pi. This reaction is catalysed by the enzyme ATP Hydrolase
84
Give two ways in which the hydrolysis of ATP is used in cells
* The hydrolysis of ATP releases energy, so this energy can be used to provide energy for energy requiring reactions within cells.
* The hydrolysis of ATP releases an inorganic phosphate, which can be used to phosphorylate other molecules in the cell, making them more reactive.
85
How is ATP is resynthesised in cells?
ADP + Pi → ATP. This is a condensation reaction, and therefore releases a molecule of water. This is hydrolysed by the enzyme ATP Synthase and it occurs during respiration and photosynthesis.
86
Suggest how the properties of ATP make it a suitable immediate source of energy for cells
* Releases energy in small, manageable amounts
* Hydrolysis of ATP is a single reaction as only one bond is hydrolysed to release energy. This means that the energy is released immediately.
* ATP molecules can not exit the cell
87
Explain how hydrogen bonds occur between water molecules
Water is a polar molecule. The slightly negatively charged oxygen atoms attract the slightly positively charged hydrogen atoms of other water molecules.
88
Explain the Specific Heat Capacity of Water
Due to the Hydrogen bonding, water molecules take more energy to separate them, so the boiling point is higher than expected. As water therefore has a higher specific heat capacity, it is a buffer to sudden temperature changes. This is important when organisms are mostly water
89
Explain the Latent Heat of Vaporisation of Water
The Hydrogen Bonding also means that a lot of energy is required to evaporate1g of water. This means that sweat in mammals is a vey efficient way of cooling as body heat is used to evaporate water.
90
Explain Cohesion and Surface Tension in Water
Cohesion allows water to be pulled through tubes e.g. xylem vessels. Where water molecules meet the air, they are pulled back to the body of water, resulting in surface tension. This allows water to support small organisms.
91
Give 3 ways that water is important to living organisms
* Metabolite - Water is used in hydrolysis and released in condensation, as well as it being a raw material in photosynthesis
* Solvent - Water dissolves gasses, wastes, ions and small hydrophilic molecules.
* Other - Evaporation cools organisms, isn’t easily compressed so allows turgor in plants, transparent so aquatic plants can photosynthesise.
92
Describe the role of Hydrogen ions
They maintain pH levels in the body, therefore affecting enzyme action.
93
Describe the role of Iron ions
They are a component of haemoglobin, therefore allowing oxygen to bind for transport as oxyhaemoglobin.
94
Describe the role of Sodium ions
They are involved in the co-transport of glucose and amino acids into cells. They are also involved in action potentials in neurons and they affect the water potential of cells, causing osmosis into and out of the cell.
